Sensing circuit including polarity discriminator

ABSTRACT

A sensing circuit using a polarity discriminator with feedback means for selecting one polarity component of a bi-polar nonsymmetrical waveshape signal input, while rejecting the opposite polarity component. The circuit operates on both the amplitude and the frequency characteristics of the input signal to produce an output signal responsive to these characteristics. The circuit may be used to process signals generated from toothed wheels by electromagnetic sensors, or the like, typically used in tachometer control.

United States Patent [1 1 Woyton [54] SENSING CIRCUIT INCLUDING POLARITY3,697,782 10/1972 Matouka............................. 328/118 FOREIGNPATENTS OR APPLICATIONS DISCRIMINATOR Joseph T. Woyton, South Bend, Ind.

Reliance Electric Company, Mishawaka, Ind.

Jan. 31, 1974- 1,280,306 10/1968Germany.......,....................307/236 [75] lnventor:

Primary ExaminerRobert S egal [73] Assignee:

Attorney, Agent, or Firm-Marmaduke Hobbs [22] Filed:

[ 7] ABSTRACT A sensing circuit using a polarity discriminator withfeedback means for selecting one polarity component 21 Appl. No.:438,232

[52] US. 328/118; 307/236; 324/165 T;

32 of a bi-polar non-symmetrical waveshape signal input, H03K 5/20 whilerejecting the opposite polarity component. The circuit operates on boththe amplitude and the frequency characteristics of the input signal toproduce an output signal responsive to these characteristics.

51 Int.

[58] Field of Search 324/165, 166, 173, 174;

5 References Cited The circuit may be used to process signals generatedUNITED STATES PATENTS from toothed wheels by electromagnetic sensors, or

the like, typically used in tachometer control.

3,210,570 /1965 Brock et a1. 328/118 X 3,247,456 4/1966 Doketer 324/1744 Claims, 8 Drawing Figures SUMM/NG c/U/VC TION 1 I, l I l 1 SUPPI. YVOL T E OUTPUT T.

AMP

I g 1 :1 L

US. Patent Oct. 28, 1975 Sheet 2 of5 3,916,326

@M EMA WW I US. Patent -Oct.28, 1975 Sheet3of5 3,916,326

US. Patent Oct. 28, 1975 Sheet4of5 3,916,326

P l| .l Illl Flllll 9w QEREMQ wok YESSVOQQ \KEEQQ mm Sq SENSING CIRCUITINCLUDING POLARITY DISCRIMINATOR This invention relates to sensingcircuits and more particular to a method of sensing both magnitude andpolarity of a'waveshape generated by a suitable sensor.

The motion of objects past a sensing point can be determined bymonitoring the output of a sensorplaced near an object in motion. Anelectrical'output will be generated from the sensor each time the movingobject passes the sensing point. The amplitude of the electrical outputsignal will be proportional to the speed of the object in motion. Thefrequency of the electrical output will be proportional to the rate atwhich the first object leaves the sensing point and another similarmoving object enters the sensing point. Rotating shaft speed monitorshave been constructed using a symmetrical toothed metallic gear attachedto the shaft, with teeth placed adjacent to a magnetic sensor. Thesensor output for such a scheme will be a symmetrical alternatingvoltage of amplitude proportional to gear tooth speed past the sensingpoint, and a frequency proportional to the rate of tooth passing. Ifthis voltage is measured, it will provide an indication of speed. Ifthis frequency is measured, it will also provide an indication of speed.Neither measurement will provide an indication of which direction,clockwise or counterclockwise, that the shaft is rotating.

An object of this invention is to provide a simple and 'reliable circuitarrangement that will enable the sensing and determination of both speedand direction of rotation.

Non-symmetrical teeth have been used on speed sensing gears to providean indication of direction of rotation of the gear teeth passing themagnetic sensor. The sensor output for such a scheme will be a voltageamplitude proportional to speed, a frequency proportional to the rate oftooth passing and a nonsymmetrical waveshape indicative of gear toothgeometry and direction of rotation. The voltage amplitude and frequencywill be indicative of rotational speed. The signal waveshape will have alarger positive peak amplitude, or a larger negative peak amplitude,depending upon the direction of tooth rotation. waveshape analysis willshow the signal characteristics inverted when the direction of rotationis reversed, thereby providing direction sensing. Dual positive andnegative averaging detectors are not useful as waveshape discriminators,since the average amplitudes are identical for both the positive andnegative portions of the sensor electrical signal, regardless ofwaveshape. Dual positive and negative peak detectors with a summingjunction have been used as waveshape discriminators. These areinefficient, since the algebraic sum of the positive and negative peaksis the resultant output. This sum is considerably less than theamplitude of either the positive or the negative component consideredseparately.

Another object of this invention is to provide an efficient method ofwaveshape discrimination for purposes of indicating the direction ofrotation of a nonsymmetrical tooth pulse wheel.

Peak detectors with fixed level logic elements are useful as waveshapediscriminators to sense whether the positive or the negative portion ofthe waveform has greater peak amplitude, thereby providing rotationaldirection sensing. These devices have the disadvantage of limiteddynamic range and would be subjected to considerable overload as boththe desired and the undesired signal polarity components'increase inamplitude as the rotational speed increases.

Another object of this invention is to provide a peak leveldiscriminator which employs a feedback means to inhibit the undesiredsignal polarity, with the inhibit function increasing or decreasing asthe incoming signal increases or decreases in amplitude with rotationalspeed, thereby continually compensating for changes in the amplitude ofthe undesired signal polarity.

Magnetic sensors in conjunction with rotating gears have been used astachometers to generate a speed signal for control purposes to regulatemotor speed. Systems of this type require selection of either a positivesignal output or a negative signal output from the sensor, dependingupon the motor rotation direction. Proper tachometer polarity isessential for proper operation of the servo loop in the speed controlcircuits. Sensor polarity is selected manuallyto coincide with the motordirection selected. A system of this type can have unstable operationwhen a rotation reversal is switched by the operator. Mechanical andelectrical lags in the system can result in the sensor tachometerfeedback signal going out of phase with the speed reference signal. Themotor could then operate at full maximum speed, inan uncontrolledopen-loop fashion since direction tracking and polarity correlation hasbeen lost for the servo loop.

Another object of this invention is to provide a system for automatictracking of speed and direction of rotation and automatic selection ofproper sensor sigal polarity. In certain instances it is desirable touse an AC tachometer generator frequency as the control signal in aspeed monitoring system. Critical applications may be unable to toleratethe uncertainties of amplitude calibration, long term sensitivitychanges, or uncompensated thermal variations that can cause errors inanalog system processing. These critical applications will rely on thefrequency of an AC tachometer generator as the control signal for thespeed monitoring system. Tachometer frequency will be stable, notsubject to calibration drift or thermal variations encountered in analogamplitude control systems. V l

Another object of this invention is to provide a system for monitoringspeed and direction of rotation, where signal frequency is controllingparameter.

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIGS. 1 and la show an arrangement of an electromagnetic pick-up coiland non-symmetrical metallic toothed gear comprising a non-symmetricalwave generating system.

FIGS. 2, 2a and 2b are a logic diagram of an arrangement in accordancewith the invention, for providing an output indicative of both speedanddirection, where input amplitude is a controlling parameter anddiagrams showing the wave for forward and reverse rotation.

FIG. 3 is an alternate logic block diagram in accordance with theinvention, where, input signal frequency is a controlling parameter.

FIG. 4 is a circuitdiagram of the logic elements in FIG. 2.

FIG. 5 is a circuit diagram of the logic elements in FIG.- 3.

Referring more specifically to the diagram of FIGS. 1 and 1a rotation ofshaft 12 of motor 17 will cause rotation of the toothed pulse wheel 14.As a wheel tooth passes the pole face 15 of the magnetic pick-up coil16, this results in a change of clearance gap 13. This gap changemodulates the magnetic flux in the pick-up coil 16, causing anelectrical voltage to 'be generated on output line 10. This voltagewaveshape will follow the flux'change characteristics of the magneticcircuit. If

pulse wheel 14 rotates clockwise past the pole face 15,

an abrupt decrease will occur in the clearance gap as the steep side ofthe pulse wheel tooth enters the pole face sensing region. This resultsin an abrupt increase of magnetic circuit flux. Accordingly, the fluxwill gradually decrease as the tooth rotation continues and the taperedside of the pulse wheel tooth now passes the pole face. Another abruptflux increase occurs as the steep side of the next tooth enters theproximity of the pole face, and the cycle continues, If the toothedwheel rotates counterclockwise, the flux change is reversed and anabrupt flux decrease is followed by a gradual flux increase.

Theoretical analysis of flux and voltage conditions in electromagneticcircuits will show that voltage amplitude is related to flux change rateand voltage polarity is related to flux change direction. Theserelationships cause non-symmetrical waveshapes of unequal peakamplitudes to appear on output line as the toothed wheel rotates.Reversing the direction of toothed wheel rotation results in waveforminversion.

Referring to the diagram of FIGS. 2, 2a and 2b, nu-

I meral 10 designates the output line of any nonsymmetrical wavegenerating system, consisting of a motor 17 with rotating shaft 12, uponwhich is mounted .a non-symmetrical toothed metallic wheel 14. Thiswheel rotates past an electro magnetic pick-up coil 16, therebygenerating a non-symmetrical electrical waveshape signal on output line10. Typical signal waveshapes for such a wave generator are shown by 34for forward rotation and 36 for reverse rotation of the toothed wheel.Either signal waveshape 34 or 36 is applied via line 10, to the puslepolarity discriminator 18. Assuming that rotation is such that waveshape34 is generated, V(+) is larger than V and both signals are passedsubstantially unimpeded thru the polarity discriminator 18 to the dualpeak detector 20. The peak detector converts the peak values of theinput waveshape to two DC voltages equal in polarity and amplitude to Vand V 7 Both outputs of the dual peak detector are applied to summingjunction 11 for combination into a net signal of amplitude (V(+) (V().This net signal is applied to the non-inverting input of amplifier 22.The amplifier gain, as set by resistors 28 and 30, is sufficient toprovide a voltage on amplifier output line 32 that is greater than anyamplitude on sensor output line 10, thus compensating for the inherentsignal losses in pulse polarity discriminator 18, dual peak detector 20and summing junction 11. The voltage from the amplifier output line 32is applied via the inhibit feedback line 26, to the polaritydiscriminator 18. This feedback action suppresses the lesser amplitudesignal V(-) of waveshape 34, and the summing junction output now risesto V(+), since V() has beensuppressed. The circuit now exhibits goodconversion efficiency at output line 32, since the degradation factorV() has been removed, and will follow peak amplitude changes of V(+)appearing on sensor output line 10 while rejecting V() components. Ifrotation of toothed wheel 14 was opposite to that described above,waveshape 36 would appear on line 10. The circuit would operatesimilarly and V(+) would be suppressed. The output 32 will now followpeak amplitude changes of V() and reject the V(+) component. The outputline 32 would be applied to a dual polarity voltage indicator 24 toregister speed and direction, or used to perform some other circuitfunction such as-to control a servo loop.

Referring now to the diagram of FIG. 3, numerals 10, l2, l4, 16, 17, 18,22, 24, 26, 28, 30 and 32 designate elements previously described. Thisarrangement of FIG. 3 differs from FIG. 2 in that elements 19, 21, 23,25, 27, 29, 31, 33, 35 and 39 establish that the input signal frequencyis a controlling parameter. Assuming that toothed wheel 14 rotationdirection is such that V(+) exceeds V() at sensor output line 10, V(+)will first overcome the operating threshold of the polaritydiscriminator 18, and appear at the discriminator output lines 19 and39. This output is applied to both positive amplifier 21 and negativeamplifier 31. Biasing arrangements provide that only positive amplifier21 will respond to the positive V(+) signal from output line 19.Amplifier 21 sharpens the waveform edges and passes the signal todifferentiator 23 which produces a sharp trigger pulse for the positivemonostable multivibrator 25. This multivibrator produces a singleuniform output pulse for each trigger pulse. This series of uniformpulses are applied to the summing junction and filter 27 where they areconverted into a DC voltage on output line 29 for amplification byamplifier 22. The gain of amplifier 22 is set by resistors 28 and 30such that the signal on line 32 is greater in amplitude than any signalor. sensor output line 10, thereby effectively compensating for theinherent losses in polarity discriminator 18, amplifier 21,differentiator 23, positive multivibrator 25, and summing junction andfilter 27. The output signal on line 32 is applied via the inhibitfeedback line 26 to the polarity discriminator 18. This feedbacksuppresses the V() signal component from sensor output line 10 in thepolarity discriminator l8 and prevents any further V() signal componentfrom appearing on discriminator output lines 19 and 39. This suppressionprevents the activation of negative amplifier 31 and the output signalon line 32 will be a DC voltage of positive polarity following thefrequncy of the V(+) component of pick-up coil 16 output. Accordingly,if toothed wheel 14 rotation is reversed from the previousconsideration, the V() component on the sensor output line 10 will beused to activate negative amplifier 31, differentiator 33, negativemonostable multivibrator 35 and summing junction and filter 27. Circuitconditions will suppress the V(+) component on the sensor output line 10in the polarity discriminator 18. Circuit elements 21, 23 and 25 willthus remain inactive, being insensitive to V() components. The outputsignal on line 32 will now be a DC voltage of negative polarity,following the frequency of the V() component of pick-up coil 16 output.

Referring to the diagram of FIG. 4, a detailed description will be givenfor a speed sensing circuit where signal amplitude is a controllingparameter. Assuming again that rotation is such that V(+) is larger thanV() on pick-up coil 16 output line 10, this signal is appliedsimultaneously to resistors 1 and 2 in the polarity discriminator. Diode7 clips the V() signal component dance created by resistor 5. Diode 4creates negligible I loading on the V() component because of therelatively high impedance created by resistor 6. The now separated V(+)and V(') components are passed individually thru diode 37 and diode 38,respectively, for peak detection by capacitors 41 and 42. The DC levelon capacitor 41 is now substantially the peak value of V(+) and the DClevel on capacitor 42 is now substantially the peak value of V(). BothDC voltages are applied to the high impedances of resistors 43 and 44 inthe summing junction 11, and the net output is obtained across resistor40 to signal common 9. Since the assumption was that V(+) was largerthan V(), the

summing junction output K (V(+) (V() will be av positive voltage to thenominverting input of amplifier 22. The gain of amplifier 22, as set byresistors 28 and 30, is sufficient to overcome all circuit losses,including the attenuation factor K of the summing junction 11. Theamplified positive DC voltage at output line 32 is now applied byfeedback line 26 to the polarity discriminator 18. The feedback signaldoes not flow through resistor 5 because diode 3 is reverse biased forpositive signals. The feedback signal, thus, does not affeet the V(+)signal component on diode 7 in the polarity discriminator. The feedbacksignal from feedback line 26 does flow through resistor 6 because diode4 is forward biased for positive signals. This feedback signal resultsin a constant forward bias on diode 8, thereby additionally suppressingthe undesired V(-) signal component at diode 8. This suppression of theV() component causes a still larger net positive output across resistor40 in the summing junction 11. The resultant increases of positivesumming junction output, leads to additional positive output onamplifier output line 32 and additional positive inhibit feedback online 26, until the entire V() component has been suppressed at diode 8in the polarity discriminator 18. The circuit has thus automaticallyselected V(+) as the proper signal polarity indicative of rotationdirection, and will continue to follow changes of rotational speedslightly. forwardbiased thru resistor 45 and resisotr 46 respectively.This initialsli ght forward bias is to prevent very low 'speed, lowamplitude signals from erroneously activating the polarity discriminatorl8. As the signal on line 10 increases with increase in speed, V(+) isfirst to overcome this initial bias threshold on diode 7, Diode 7 clipsall V componentson its cathode to signal common 9 'and only allows V(+)components that exceed the initial bias threshold. The V(+) signals arethen applied by line 19 to the positive amplifier 21. This amplifiershapes the edges of the V(+) pulsed signal and serves as an input signallimiter. The amplifier operation is common in the art and its functionneed not be described further. The sharp edged V(+) pulse is applied todifferentiator 23, which triggers positive monostable multivibrator 25.This multivibrator then delivers a uniform positive output pulse foreach cycle of the V(+) input frequency. These uniform pulses arefiltered and averaged by the summing junction and filter 27. Operationof the differentiator 23, multivibrator 'and summing junction and filter27 are common in the art, and their operation need not be describedfurther. The resultant filtered DC voltage from 27 is applied by line 29to the noninverting input of amplifier 22. The gain of amplifier 22, asset by resistors 28 and 30 is such that the output at line 32 exceedsany signal in pick-up coil output line 10. The amplified positive outputat line 32 is applied by the inhibit feedback line 26 to the polaritydiscriminator 18. The inhibit signal does not flow through diode 3 orresistor 5 because diode 3 is reverse biased for this positive signal.The

V(+) signal conditions are thus undisturbed at diode 7.

. and generate a positive DC voltage proportional to this for thatdirection. The output at line 32 will be a positive DC voltageproportional to rotational speed. This output signal can now be used toindicate speed and direction of rotation, or serve other control systemfunctions. If initial rotation was assumed in the opposite direction,V(-) would exceed V(+) and the system would accordingly control on onlythe V() component from pick-up coil 16 and suppress all V(+) componentsin the polarity discriminator 18. If the rotation should make atransition from one speed, through zero, to some speed in the oppositedirection, the circuit will track the first speed and polarity reset thepolarity selection at zero speed, and again track the opposite speedwith proper reversed polarity.

Referring to FIG. 5, a detailed description will now be given for aspeed sensing circuit in which signal frequency is a controllingparameter. Assuming again that rotation direction is such that V(+)exceeds V() on pick-up coil 16 output line 10. This signal issimultaneously applied to resistor l and resistor 2 in the polaritydiscriminator l8. Diode 7 and diode 8 are both frequency. lf rotationdirection established that V(-) exceeds V(+) on output line 10, thecircuit accordingly would now follow the frequency of the V() signalonly, suppressing all V(+) components, and generate a negative DCvoltage proportional to this frequency.

It is seen that the sensing circuit in accordance with I the inventionautomatically selects the larger amplitude polarity of an input bi-polarnon-symmetrical wavemade to satisfy requirements. Systems usingcapacitive sensors and companion wheels as well as optical shutters withphotoelectric sensors will serve equally well to 1. A sensing circuitcomprising a means for producing a bi-polar, non-symmetrical waveshapesignal, a po- 2. A sensing circuit as defined in claim 1 in which saidfirst mentioned means includes a non-symmetrical toothed wheel and acompatible sensor.

3. A sensing circuit as defined in claim 1 in which said signalprocessing circuit generates a DC voltage in response to said signalamplitude.

4. A sensing circuit as defined in claim 1 wherein said feedback meansincludes diodes.

1. A sensing circuit comprising a means for producing a bipolar,non-symmetrical waveshape signal, a polarity discriminator connected tosaid means, a bipolar signal processing circuit including a dual peakdetector, summing junction, and noninverting amplifier, said circuitbeing connected to said discriminator and controlled by the amplitude ofsaid signal, a feedback means connecting said bi-polar signal processingcircuit to said polarity discriminator for selecting one polaritycomponent of said signal input, while rejecting the opposite polaritycomponent.
 2. A sensing circuit as defined in claim 1 in which saidfirst mentioned means includes a non-symmetrical toothed wheel and acompatible sensor.
 3. A sensing circuit as defined in claim 1 in whichsaid signal processing circuit generates a DC voltage in response tosaid signal amplitude.
 4. A sensing circuit as defined in claim 1wherein said feedback means includes diodes.